ldd: implement strict ldd output parser

Fortify needs to internally resolve helper program sandbox config. They are considered trusted and runs under the privileged UID so ldd output is used to determine libraries they need inside the sandbox environment.

Signed-off-by: Ophestra Umiker <cat@ophivana.moe>

ldd/error.go

@@ -0,0 +1,11 @@
+package ldd
+
+import "fmt"
+
+type EntryUnexpectedSegmentsError struct {
+	Entry string
+}
+
+func (e *EntryUnexpectedSegmentsError) Error() string {
+	return fmt.Sprintf("unexpected segments in entry %q", e.Entry)
+}

ldd/ldd.go

@@ -0,0 +1,84 @@
+package ldd
+
+import (
+	"errors"
+	"fmt"
+	"math"
+	"os"
+	"os/exec"
+	"path"
+	"strconv"
+	"strings"
+)
+
+var (
+	ErrUnexpectedSeparator = errors.New("unexpected separator")
+	ErrPathNotAbsolute     = errors.New("path not absolute")
+	ErrBadLocationFormat   = errors.New("bad location format")
+)
+
+type Entry struct {
+	Name     string `json:"name,omitempty"`
+	Path     string `json:"path,omitempty"`
+	Location uint64 `json:"location"`
+}
+
+func Exec(p string) ([]*Entry, error) {
+	t := exec.Command("ldd", p)
+	t.Stdout = new(strings.Builder)
+	t.Stderr = os.Stderr
+
+	if err := t.Run(); err != nil {
+		return nil, err
+	}
+
+	out := t.Stdout.(fmt.Stringer).String()
+	payload := strings.Split(out, "\n")
+
+	result := make([]*Entry, len(payload))
+
+	for i, ent := range payload {
+		if len(ent) == 0 {
+			continue
+		}
+
+		segment := strings.SplitN(ent, " ", 5)
+
+		var iL int
+
+		switch len(segment) {
+		case 2: // /lib/ld-musl-x86_64.so.1 (0x7f04d14ef000)
+			iL = 1
+			result[i] = &Entry{Name: segment[0]}
+		case 4: // libc.musl-x86_64.so.1 => /lib/ld-musl-x86_64.so.1 (0x7f04d14ef000)
+			iL = 3
+			if segment[1] != "=>" {
+				return nil, ErrUnexpectedSeparator
+			}
+			if !path.IsAbs(segment[2]) {
+				return nil, ErrPathNotAbsolute
+			}
+			result[i] = &Entry{
+				Name: segment[0],
+				Path: segment[2],
+			}
+		default:
+			return nil, &EntryUnexpectedSegmentsError{ent}
+		}
+
+		if loc, err := parseLocation(segment[iL]); err != nil {
+			return nil, err
+		} else {
+			result[i].Location = loc
+		}
+	}
+
+	return result, nil
+}
+
+func parseLocation(s string) (uint64, error) {
+	if len(s) < 4 || s[len(s)-1] != ')' || s[:3] != "(0x" {
+		return math.MaxUint64, ErrBadLocationFormat
+	}
+	return strconv.ParseUint(s[3:len(s)-1], 16, 64)
+}